Highly stable aqueous solution of partially saponified vinyl ester resin

ABSTRACT

An aqueous solution of partially hydrolyzed vinyl ester resin having an excellent stability and useful particularly as a secondary agent for suspension polymerization of vinyl compounds, wherein the partially hydrolyzed vinyl ester resin has a degree of hydrolysis of at most 70% by mole, it is contained in a concentration of at most 50% by weight, and it satisfies the equation: 1n y&gt;0.042x+1.0, in which y is the cloud point (° C.) of a 30% by weight aqueous solution of the partially hydrolyzed vinyl ester resin, and x is the degree of hydrolysis (% by mole) of the partially hydrolyzed vinyl ester resin.

TECHNICAL FIELD

The present invention relates to an aqueous solution of a partiallyhydrolyzed vinyl ester resin which does not cause phase separation,deposition, gelation and the like of the partially hydrolyzed vinylester resin in the aqueous solution and has an excellent stability.

BACKGROUND ART

Partially hydrolyzed vinyl ester resins having a degree of hydrolysis ofat most 70% by mole have been widely utilized as primary dispersingagents or secondary dispersing agents for suspension polymerization ofvinyl compounds (particularly vinyl chloride), binders, plasticizers orhot melt adhesives.

However, partially hydrolyzed vinyl ester resins having a degree ofhydrolysis of at most 70% by mole, in particular alkalihydrolyzed vinylester resins having a degree of hydrolysis of at most 67% by mole, arecompletely insoluble in water. Therefore, when these resins are used forexample as a secondary agent for suspension polymerization, in generalthey are added in the form of a powder or they are dissolved in awater-alcohol solvent or water-ketone solvent and then added. The formerprocedure is poor in charging workability and also the effects as thesecondary agent are not sufficiently exhibited. The latter procedure mayraise a problem of environmental pollution (increase of BOD and CODloads) owing to alcohol solvent.

In order to solve such problems, proposed is a method using an aqueousdispersion containing as a dispersoid a vinyl ester polymer having aminogroup, ammonium group, carboxyl group or sulfo group in the side chains(Japanese Patent Publication Kokai No. 4-154810). It is also proposed touse, as a dispersion stabilizer, one or more water-soluble polyvinylalcohols prepared by partial solvolysis of polyvinyl acetate in analcoholic solution containing an acid catalyst (Japanese PatentPublication Kokai No. 56-104912). The present applicant also proposed adispersion stabilizer comprising a vinyl ester resin having anoxyalkylene group in the polymer side chains and a water-soluble highmolecular compound (Japanese Patent Publication Kokoku No. 3-60321).

However, according to the technique disclosed in Japanese PatentPublication Kokai No. 4-154810, there is a case where itscharacteristics (improvement in porosity, uniformity of porositydistribution, monomer removability, plasticizer absorptivity and thelike of obtained polymers of vinyl compounds) cannot be sufficientlyexhibited, the reason of which is assumed to be that the pH range (3 to8) of the polymerization system varies depending on the amount of abuffer used in the polymerization of vinyl compounds, the opportunity ofcharging the buffer, the oxygen concentration of the polymerizationsystem and the like. Further, when used as a secondary agent forsuspension polymerization of vinyl monomers, there arises a problem thatthe suspension polymerization becomes unstable to result in productionof coarse particles of polymers, the cause of which is assumed to bethat protective colloid characteristics of a primary agent are loweredby the secondary agent since the hydrophilic property becomes strong.The technique disclosed in Japanese Patent Publication Kokai No.56-104912 has the disadvantages that if the degree of hydrolysis of thepolyvinyl alcohol is less than 55% by mole, it is completely insolublein water and is unsuitable, and if the degree of hydrolysis is from 55to 60% by mole, the aqueous solution thereof is stable at aconcentration as high as 30 to 40% by weight, but the polyvinyl alcoholis deposited when diluted to a concentration of less than 30% by weight.It has also the disadvantages that the aqueous solution is easy to causephase separation into two layers when stored because of low cloud pointand that it is poor in workability in handling. In case of the techniquedisclosed in Japanese Patent Publication Kokoku No. 3-60321, it is notpossible to prepare an aqueous solution having a high resinconcentration of not less than 30% by weight and, also, the storagestability is bad. Further, even in aqueous solutions having a low resinconcentration, the resin may be deposited and, therefore, inconvenienceis expected also when used as a secondary agent.

DISCLOSURE OF THE INVENTION

The present inventors have found, as a result of intensive study made inview of such circumstances, that an aqueous solution containing at most50% by weight of a partially hydrolyzed vinyl ester resin which has adegree of hydrolysis of at most 70% by mole and which satisfies theequation (I):

1n y>0.042x+1.0  (I)

wherein y is a cloud point (° C.) of the 30% by weight aqueous solutionthereof and x is the degree of hydrolysis (% by mole) thereof, isexcellent in stability of aqueous solution even if diluted to a lowconcentration of not more than 30% by weight, to say nothing of under ahigh concentration, and is suitable for use as secondary agent forsuspension polymerization, binders for various purposes, plasticizer andthe like, and that particularly in case of using as a secondary agentfor suspension polymerization, appearance of cloud point is suppressed(miscibility with water is good) when used at ordinary temperature andno deposition occurs even if the resin concentration of the aqueoussolution is as low as not more than 30% by weight, thus the solution isparticularly excellent in storage stability, and further that when suchan aqueous solution is added as a secondary agent to a polymerizationsystem for suspension polymerization of vinyl compounds, it is assumedthat the secondary agent can immediately exhibit an oil solubility as apartially hydrolyzed vinyl ester resin since perhaps the secondary agentcannot sufficiently include water molecules at a concentration of lessthan 1% by weight, so it is adsorbed by or dissolved in the vinylmonomers and, therefore, polymerization products having excellentplasticizer absorptivity and monomer removability are obtained withoutbeing affected by the polymerization conditions such as amount of abuffer used in the polymerization of vinyl compounds and pH change inthe polymerization system owing to oxygen concentration or the like ofthe polymerization system. Thus, the present inventors have accomplishedthe present invention.

In accordance with the present invention, there is provided an aqueoussolution of a partially hydrolyzed vinyl ester resin having an excellentstability, characterized by containing a partially hydrolyzed vinylester resin having a degree of hydrolysis of at most 70% by mole in aconcentration of at most 50% by weight, said partially hydrolyzed vinylester resin satisfying the equation (I):

1n y>0.042x+1.0  (I)

wherein y is the cloud point (° C.) of a 30% by weight aqueous solutionof said partially hydrolyzed vinyl ester resin, and x is the degree ofhydrolysis (% by mole) of said partially hydrolyzed vinyl ester resin.

BEST MODE FOR CARRYING OUT THE INVENTION

The partially hydrolyzed vinyl ester resins used in the presentinvention are not particularly limited so long as they have a degree ofhydrolysis of at most 70% by mole, and the cloud point y (° C.) of a 30%by weight aqueous solution thereof and the degree of hydrolysis x (% bymole) thereof satisfies the equation (I):

1n y>0.042x+1.0  (I)

Preferably, the degree of hydrolysis of the partially hydrolyzed vinylester resins is from 0 to 60% by mole, especially from 20 to 60% bymole, more especially from 30 to 60% by mole. If the degree ofhydrolysis exceeds 70% by mole, the monomer removability, uniformity ofporosity distribution and improvement in plasticizer absorptivity ofpolymers of vinyl compounds obtained by suspension polymerization usingthe partially hydrolyzed vinyl ester resins as a secondary agent areinsufficient. Also, the partially hydrolyzed vinyl ester resins arepreferred to be those satisfying the equation (II):

1n y>0.042x+1.7  (II)

wherein y is the cloud point (° C.) of a 30% by weight aqueous solutionthereof and x is the degree of hydrolysis (% by mole) thereof. If thepartially hydrolyzed vinyl ester resins do not satisfy the equation (I),the aqueous solution is inferior in storage stability at a highconcentration and a cloud point appears under some storage conditions,and also when used as a secondary agent for suspension polymerization ofvinyl compounds, the characteristics such as particle size distribution,monomer removability and plasticizer absorptivity of the obtained vinylpolymers are lowered.

Control of the relationship represented by the equation (I) can beachieved by introducing a bulky hydrophilic group into the molecule of apartially hydrolyzed vinyl ester resin to thereby adjust a balancebetween the degree of hydrolysis and the degree of polymerization. Asthe partially hydrolyzed vinyl ester resin to which a hydrophilic grouphas been introduced, preferred are those containing a functional groupof the formula (1):

wherein R¹, R², R³ and R⁴ are a hydrogen atom or an alkyl group, X¹ andX² are an oxygen atom or a sulfur atom, n is a positive number and m is0 or a positive number.

In the formula (1), preferable ranges of n and m are represented by therelationship of 5≦n+m≦50, especially 8≦n+m≦20. If n+m is less than 5,the aqueous solution of partially hydrolyzed vinyl ester resin is poorin stability. Thus, for example, if a 40% by weight aqueous solution ofsuch a partially hydrolyzed vinyl ester resin having a degree ofhydrolysis of 60% by mole is diluted to a low concentration of 3 to 20%by weight, the partially hydrolyzed vinyl ester resin is deposited.Also, the cloud point is lowered, so the above-mentioned equation (I)cannot be satisfied. If n+m is more than 50, contribution as a oilsoluble component is hard to appear since the hydrophilic propertybecomes too strong, so the effects as secondary agent cannot besufficiently exhibited. Also, from the industrial point of view,production cost rises.

The partially hydrolyzed vinyl ester resins having functional groups (1)can be prepared by any methods, for example, (i) a method wherein avinyl ester is polymerized in the presence of a polyoxyalkylene polymerand the resulting polymer is then hydrolyzed, (ii) a method wherein avinyl ester is copolymerized with an unsaturated monomer having thefunctional group (1) and the resulting polymer is then hydrolyzed, (iii)a method wherein a partially hydrolyzed vinyl ester resin is subjectedto a post reaction with an alkylene oxide, (iv) a method whereinethylene oxide, propylene oxide or the like is addition-polymerized to avinyl ester resin (in a preferable embodiment, ethylene oxide andbutylene oxide are addition-polymerized to a vinyl ester resin to formethylene oxide block-butylene oxide block-ethylene oxide block having abutylene oxide content of at most 20% by weight, preferably at most 10%by weight) in the presence of a catalyst, e.g., an acid or an alkalihydroxide such as sodium hydroxide or potassium hydroxide and theresulting polymer is then hydrolyzed, and (v) a method wherein a polymerof a vinyl ester compound, to the molecular end of which athiol-containing alkylene glycol derivative has been introduced, ishydrolyzed, the introduction being conducted in a manner such that thethiol-containing alkylene glycol derivative is made exist in thepolymerization system of the vinyl ester compound wherein the additionof the thiol-containing alkylene glycol compound may be conducted priorto starting the polymerization or at an adequate opportunity during thepolymerization. Of the above methods (i) to (v), the method (ii) ispractical from the viewpoints of the preparation and properties of theresin.

An explanation will be given below with the method (ii) as the centralfigure.

Firstly, the functional group (1) is explained.

In case that both of X¹ and X² are oxygen atom, the functional group (1)is an oxyalklylene group represented by the formula (2):

and such an oxyalkylene group is in general a group represented by theformula (3):

wherein R¹, R², R³ and R⁴ are a hydrogen atom or an alkyl group, n is apositive number and m is 0 or a positive number. Oxyalkylene groups ofthe formula (1) or (2) wherein the total number of n+m is from about 5to about 50, preferably 8 to 20, are practical. For example,(poly)oxyethylene group, (poly)oxypropylene group, (poly)oxybutylenegroup and the like are effective, and (poly)oxyethylene group ispreferable.

Unsaturated monomers having an oxyalkylene group include, for instance,the following compounds, but are not limited thereto in the presentinvention.

[(Meth)acrylic Acid Esters]

There are mentioned monomers of the following formula (4), examples ofwhich are polyoxyethylene (meth)acrylate, polyoxypropylene(meth)acrylate and the like:

wherein Y is a hydrogen atom or a methyl group, A is a phenylene groupor a substituted phenylene group, 1 is 0 or an integer of not less than1, R¹, R², R³ and R⁴ are a hydrogen atom or an alkyl group, n is apositive number and m is 0 or a positive number, provided that n+m isfrom 5 to 50, preferably from 8 to 20.

[(Meth)acrylamides]

There are mentioned monomers of the following formula (5), examples ofwhich are polyoxyethylene(meth)acrylamide,polyoxy-propylene(meth)acrylamide, polyoxyethylene( 1-(meth)acrylamide-1,1-dimethylpropyl)ester, and the like:

wherein Y³ is a hydrogen atom, a methyl group or the group (1) or (2),and A, Y, R¹, R², R³, R⁴, 1, n, m and n+m are as defined above.

[(Meth)allyl Alcohols]

There are mentioned monomers of the following formula (6), examples ofwhich are polyoxyethylene (meth)allyl ether, polyoxypropylene(meth)allyl ether and the like.

wherein Y, R¹, R², R³, R⁴, n, m and n+m are as defined above.

[Vinyl Ethers]

There are mentioned monomers of the following formula (7), examples ofwhich are polyoxyethylene vinyl ether, polyoxypropylene vinyl ether andthe like:

wherein A, R¹, R², R³, R⁴, 1, n, m and n+m are as defined above.

Of these monomers containing oxyalkylene group, (meth)allyl alcoholcompounds (6) are preferably used.

In the above-mentioned method (v) for preparing the partially hydrolyzedvinyl ester resin, a thiol group-containing alkylene glycol derivativeof the formula (8):

wherein R¹, R², R³ and R⁴ are a hydrogen atom or an alkyl group, R⁵ is ahydrogen atom or SH, X¹ and X² are an oxygen atom or a sulfur atom, andn, m and n+m are as defined above,

is introduced as the functional group (1) to a vinyl ester resin.Examples of the derivative (8) are, for instance, polyethylene glycolwhose both ends or one end is converted to SH.

In the present invention, it is preferable that the partially hydrolyzedvinyl ester resins contain the functional group (1), and those furthercontaining an ionic group are more preferred so that an aqueous solutionof the vinyl ester-vinyl alcohol copolymer can be handled in a widerange of dilution. The content of the ionic group is preferably from0.05 to 1.0% by mole, more preferably from 0.1 to 1.0% by mole.Introduction of the ionic group is conducted usually by a methodcomprising copolymerizing a vinyl ester compound with comonomers, i.e.,an unsaturated monomer having the functional group (1) and a monomerhaving an ionic group, and then hydrolyzing the resulting copolymer. Themonomer having an ionic group is not particularly limited and includes,for instance, a carboxyl group-containing monomer, a sulfogroup-containing monomer, an amino group-containing monomer, an ammoniumgroup-containing monomer and the like.

Examples of the carboxyl group-containing monomer are, for instance, anethylenically unsaturated dicarboxylic acid (such as maleic acid,fumaric acid or itaconic acid), an ethylenically unsaturateddicarboxylic acid monoester (such as a monoalkyl maleate, a monoalkylfumarate or a monoalkyl itaconate), an ethylenically unsaturateddicarboxylic acid diester (such as a dialkyl maleate, a dialkyl fumarateor a dialkyl itaconate), an ethylenically unsaturated carboxylicanhydride. (such as maleic anhydride or itaconic anhydride),(meth)acrylic acid, and salts of these monomers. Of these, ethylenicallyunsaturated dicarboxylic acids, ethylenically unsaturated carboxylicacid monoesters, and salts thereof are preferable.

The ionic group can also be introduced into vinyl ester resins by usinga compound having a functional group, e.g., an alcohol, aldehyde orthiol having carboxyl group, as a chain transfer agent. In particular,those derived from a thiol which has a large chain transferring effectare effective. Examples of the thiol are a compound of the formula (9):

HSCH₂_(n)COOH  (9)

wherein n is an integer of 0 to 5, or its salt;

a compound of the formula (10):

wherein Y is independently a hydrogen atom or a lower alkyl group whichmay contain a substituent, and n is an integer of 0 to 5, or its salt; acompound of the formula (11):

wherein n is an integer of 0 to 20, or its salt, e.g.,2-mercaptopropionic acid, 3-mercaptopropionic acid or 2-mercaptostearicacid; a compound of the formula (12):

HSCHX³_(r)(CHX⁴)_(s)COOH  (12)

wherein X³ is a hydrogen atom or a carboxyl group, X⁴ is a hydrogenatom, r is 0 or a positive number, and s is a positive number, e.g.,thioglycollic acid, thiopropionic acid or thiomalic acid; and the like.

The sulfo group-containing monomer includes, for instance, the followingcompounds.

(a) Olefin sulfonic acids such as ethylenesulfonic acid, allylsulfonicacid or methallylsulfonic acid, and salts thereof.

(b) Sulfoalkyl maleates represented by the formulas (13) and (14):

wherein R₁ is an alkyl group, n is an integer of 2 to 4, and M ishydrogen, an alkali metal or an ammonium ion. Examples of the sulfoalkylmaleates are sodium sulfopropyl 2-ethylhexyl maleate, sodium sulfopropyl2-ethylhexyl maleate, sodium sulfopropyl tridecyl maleate, sodiumsulfopropyl eicosyl maleate, and the like.

(c) Sulfoalkyl(meth)acrylamides represented by the formulas (15) to (17)and sulfoalkyl (meth)acrylates represented by the formula (18):

wherein Y², Y³, Y⁴, Y⁵, Y⁷, Y⁸ and Y⁹ are hYdrogen or an alkYl group, Y⁶is an alkyl group, n is an integer of 2 to 4, and M is hydrogen, analkali metal or an ammonium ion. Examples of thesulfoalkyl(meth)acrylamides are sodium sulfomethylacrylamide, sodiumsulfo-t-butylacrylamide, sodium sulfo-s-butylacrylamide, sodiumsulfo-t-butylmethacrylamide, and the like.

wherein Y¹⁰ is hydrogen or an alkyl group, n is an integer of 2 to 4,and M is a hydrogen atom, an alkali metal or an ammonium ion. Examplesof the sulfoalkyl (meth)acrylates are sodium sulfoethyl acrylate, andthe like.

Of the above-mentioned sulfo group-containing monomers, an olefinsulfonic acid and its salt are preferably used.

The ionic group can also be introduced into vinyl ester resins by usinga sulfo group-containing compound, e.g., an alcohol, aldehyde or thiolhaving sulfo group, as a chain transfer agent. In particular, thosederived from a thiol which has a large chain transferring effect areeffective. Examples of the thiol are compounds represented by theformulas (19) to (22):

wherein each of Y¹¹ to Y¹⁹ is a hydrogen atom or a methyl group, n is aninteger of 2 to 4, M is a hydrogen atom, an alkali metal or an ammoniumion, and n groups of each of Y¹⁴, Y¹⁵, Y¹⁷ and Y¹⁸ may be simultaneouslythe same or different. Representative examples are sodium sulfopropanethiopropionate and the like.

As a method for obtaining vinyl ester-vinyl alcohol copolymersintroduced with a sulfo group are also adoptable a method wherein avinyl ester-vinyl alcohol copolymer is treated with bromine, iodine orthe like and is then heated with an aqueous solution of sodium acidsulfite, a method wherein a polyvinyl alcohol is heated in aconcentrated aqueous solution of sulfuric acid, and a method wherein avinyl ester-vinyl alcohol copolymer is acetalized with an aldehydecompound having a sulfo group.

Examples of the amino group or ammonium group-containing monomers usedfor introducing an ionic group are, for instance, a compound of theformula (23):

or its quaternary compound;

a compound of the formula (24):

or its quaternary compound;

a compound of the formula (25):

or its quaternary compound;

a compound of the formula (26):

or its quaternary compound; and

a compound of the formula (27):

wherein n is an integer of 0 to 3, m is a positive number of 1 to 10,Y¹, Y², Y⁵, Y⁶ and Y⁷ are a hydrogen atom or a methyl group, Y³ and Y⁴are a lower alkyl group which may have a substituent, X is an anionwhich forms a salt with an ammonium nitrogen, and A is a group bondingamine or ammonium with the nitrogen atom of amido group in the compound(23) or the oxygen atom in the compound (25).

Also, adoptable is a method wherein polymerization is carried out in thepresence of a chain transfer agent such as an amino group or ammoniumgroup-containing compound, e.g., an alcohol, aldehyde or thiol compoundhaving amino group or ammonium group. In particular, those derived froma thiol compound which has a large chain transferring effect areeffective. Examples of the thiol are, for instance, a compound of theformula (28):

or its quaternary compound;

a compound of the formula (29):

or its quaternary compound;

a compound of the formula (30):

or its quaternary compound; and

a compound of the formula (31):

or its quaternary compound,

wherein n is an integer of 0 to 3, m is an integer of 1 to 10, Y¹, Y²,Y⁵, Y⁶ and Y⁷ are a hydrogen atom or a methyl group, Y³ and Y⁴ are alower alkyl group which may have a substituent, and A is a group bondingthe nitrogen atom of amine or ammonium with the nitrogen atom of amidogroup in the compound (28) or the oxygen atom in the compound (30).

Examples of a vinyl ester to be copolymerized with the above-mentionedmonomers are vinyl formate, vinyl acetate, vinyl trifluroacetate, vinylpropionate, vinyl butyrate, vinyl caprate, vinyl laurate, vinylmyristate, vinyl palmitate, vinyl stearate, vinyl pivalate, and thelike. These may be used alone or in admixture thereof. Vinyl acetate isindustrially suitable.

In the present invention, the vinyl ester compound may be copolymerizedwith at most 50% by mole, preferably at most 20% by mole, of a monomerhaving functional group (1) as mentioned above, a monomer having anionic group as mentioned above, other monomers copolymerizable with thevinyl ester compound, or a mixture thereof. Examples of the othermonomers copolymerizable with the vinyl ester compound are give below.

[Ethylenically unsatureated dicarboxylic acid alkyl esters and the like]

There are mentioned methyl crotonate, ethyl crotonate, methyl sorbate,ethyl sorbate, alkyl oleates, methyl (meth)acrylate, ethyl(meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, pentyl(meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, decyl(meth)acrylate, hexadecyl (meth)acrylate, octadecyl (meth)acrylate, andthe like.

[α-Olefins]

There are mentioned ethylene, propylene, α-hexene, α-octene, α-decene,α-dodecene, α-hexadecene, α-octadecene, and the like.

[Alkyl Vinyl Ethers]

There are mentioned propyl vinyl ether, butyl vinyl ether, hexyl vinylether, octyl vinyl ether, decyl vinyl ether, dodecyl vinyl ether,tetradecyl vinyl ether, hexadecyl vinyl ether, octadecyl vinyl ether,and the like.

[Alkyl Allyl Ethers]

There are mentioned propyl allyl ether, butyl allyl ether, hexyl allylether, octyl allyl ether, decyl allyl ether, dodecyl allyl ether,tetradecyl allyl ether, hexadecyl allyl ether, octadecyl allyl ether,and the like.

Besides, (meth)acrylamide, (meth)acrylonitrile, styrene, vinyl chlorideand the like are also usable.

Upon the copolymerization, the polymerization method is not particularlylimited, and any known polymerization methods can be suitably used. Asolution polymerization using an alcohol such as methanol, ethanol orisopropanol as a solvent is usually practiced. Emulsion polymerization,suspension polymerization and the like are also of course adoptable. Asto a manner of charging monomers in such a solution polymerization, anymanners can be used, e.g., a manner wherein a polymerization of a vinylester is started, and the remaining monomer is continuously or stepwiseadded during the polymerization period, a manner wherein a monomer isadded at one time in the initial stage of the polymerization, and amanner wherein a vinyl ester and other monomer are simultaneously addedfrom the initial stage of the polymerization. In case of conducting thepolymerization in the presence of a chain transfer agent, it ispreferable to add the chain transfer agent in accordance with the degreeof reaction of the vinyl ester in the polymerization system so that theamount of chain transfer in the reaction system does not change too muchwith respect to the vinyl ester, thereby achieving the desired degree ofmodification. The copolymerization reaction is carried out by using aknown radical polymerization initiator or low-temperature activecatalyst, e.g., azobisisobutyronitrile, acetyl peroxide, benzoylperoxide or lauroyl peroxide. The reaction temperature is selected fromthe range between about 30° C. and the boiling point of a solvent.

The vinyl ester component is converted into a vinyl alcohol component bypartially hydrolyzing it. It is necessary that the degree of hydrolysisis not more than 70% by mole. Preferably, the degree of hydrolysis isfrom 0 to 60% by mole, especially 20 to 60% by mole, more especiallyfrom 30 to 60% by mole.

Upon the hydrolysis, the copolymer is dissolved in a solvent such as analcohol, benzene or methyl acetate, and the hydrolysis is carried out inthe presence of an alkali catalyst. Examples of the alcohol aremethanol, ethanol, isopropanol, butanol and the like. The concentrationof the copolymer in the alcohol is selected from 20 to 50% by weight.

As the hydrolysis catalyst are used an alkali catalyst, e.g., ahydroxide or alcoholate of an alkali metal such as sodium hydroxide,potassium hydroxide, sodium methylate, sodium ethylate or potassiummethylate. The amount of such a catalyst is from 1 to 100 millimolarequivalents, preferably 1 to 50 millimoles, more preferably 1 to 30millimoles, per mole of the vinyl ester of the monomer units.

It is also possible to carry out the hydrolysis by using an acidcatalyst such as sulfuric acid or hydrochloric acid in order to furtherraise the storage stability of the secondary agent which comprises anaqueous solution of a partially hydrolyzed vinyl ester resin.

Thus, a partially hydrolyzed vinyl ester resin having a functional group(1) used in the present invention is obtained. The content of thefunctional group (1) is preferably from 0.5 to 5.0% by mole, morepreferably 1.0 to 4.0% by mole, still more preferably 1.0 to 3.0% bymole. If the content is less than 0.5% by mole, the storage stability ofthe aqueous solution is poor. If the content exceeds 5.0% by mole, theuniformity of the porosity distribution, porosity and plasticizerabsorptivity of vinyl resins obtained by suspension polymerization ofvinyl compounds using the partially hydrolyzed vinyl ester resin as adispersing stabilizer are lowered.

The content of the ionic group in the partially hydrolyzed vinyl esterresin in the present invention is preferably from 0.05 to 1.0% by mole,more preferably from 0.1 to 1.0% by mole. If the content is less than0.05% by mole, the storage stability is lowered when the resinconcentration of the aqueous solution is adjusted to less than 5%. Ifthe content exceeds 1.0% by mole, the stability in suspensionpolymerization of vinyl monomers is impaired to result in production ofcoarse particles of the vinyl polymers for the assumed reason that thehydrophilic property becomes strong and the protective colloidcharacteristics of a primary agent are lowered.

An aqueous solution of the partially hydrolyzed vinyl ester resin isthen prepared. The manner of obtaining such an aqueous solution is notparticularly limited, and adoptable are a manner wherein the alcoholused in the hydrolysis is replaced with water by blowing of steam or thelike, a manner wherein the vinyl ester resin is poured into water withstirring and the stirring is subsequently conducted, and such mannerscombined with heating. The manner wherein the alcohol used in thehydrolysis is replaced with water by blowing of steam or the like ispreferably used.

The thus obtained aqueous solution of partially hydrolyzed vinyl esterresin of the present invention has a transparency, a good miscibilitywith water and a high cloud point. Also, when the resin has a specificdegree of hydrolysis, for example, a degree of hydrolysis of 50% bymole, no deposition is formed even if the aqueous solution is diluted upto 2 to 3% by weight. Therefore, by utilizing the feature and the likethat it is also possible to use only the aqueous solution of the presentinvention without using an organic solvent, the aqueous solution of thepresent invention can be employed in various uses where the use oforganic solvents such as an alcohol has been conventionally required.Examples of the uses are as follows:

(1) Molded articles and related uses

film, sheet, sealing film, temporary film, and others

(2) Adhesives

adhesive for wood, paper, aluminum foil, plastics and the like,tackifier, remoistening adhesive, binder for non-woven fabric, binderfor building materials such as gypsum board and fiber board, binder forgranulation of various powders such as filler, additive for cement andmortar, hot melt adhesive, pressure sensitive adhesive, anchoring agentfor anionic paints, and others

(3) Covering materials and related uses

clear coating material for paper, pigmented coating material for paper,OHP coating material, internal sizing agent for paper, sizing agent fortextile goods, weft sizing agent, fiber processing agent, leatherfinishing agent, paint, anticlouding agent, metal corrosion inhibitor,glazing agent for galvanization, antistatic agent, conducting agent,temporary paint, and others

(4) Blending agents for hydrophobic resins and related uses

antistatic agent for hydrophobic resins, hydrophilic property-impartingagent, additive for films and other molded articles, compatibilizer,plasticizer, and others

(5) Dispersing stabilizer for suspension and related uses

pigment dispersing agent for paints, black writing fluid, water color,adhesive and the like, primary dispersing agent or secondary dispersingagent for suspension polymerization of vinyl chloride, styrene,methacrylic acid esters, vinyl acetate and the like, and others

(6) Dispersing stabilizer for emulsion and related uses

emulsifier for emulsion polymerization of ethylenically unsaturatedcompounds and butadienic compounds, post-emulsifying agent forhydrophobic resins such as polyolefins and polyester resins, epoxyresins, paraffin, bitumen and the like, and others

(7) Thickener and related uses

thickener for various aqueous solutions and emulsions, and others

(8) Coagulating agent and related uses

coagulating agent for suspensoid and dissolved matter in water, andothers

(9) Soil improver and related uses

(10) Uses related to photosensitive agent, electronics andphotosensitive

resist resin

Of the above-mentioned uses, the aqueous solution of partiallyhydrolyzed vinyl ester resin of the present invention is particularlyuseful as a secondary agent for suspension polymerization of vinylcompounds. A process of the suspension polymerization of vinyl compoundsusing such an aqueous solution will be explained below.

The above-mentioned partially hydrolyzed vinyl ester resin dispersed ordissolved in water in a concentration of at most 50% by weight,preferably 1 to 45% by weight, more preferably 3 to 40% by weight, isused as the secondary agent. If the concentration of the resin exceeds50% by weight, unsuitable matter may occur, for example, the fluidity ofthe aqueous solution is markedly deteriorated or the aqueous solution isgelled.

The secondary agent comprising the aqueous solution of the presentinvention has a good storage stability of not less than one year withoutparticularly using a dispersing agent or an emulsifying agent.

Also, the aqueous solution of the present invention may contain anadequate amount of a known preservative such as sodium dehydroacetate,potassium sorbate or pentachlorophenol sodium salt within the range thatthe performances as the secondary agent are not impaired.

As a partially hydrolyzed vinyl ester resin in the secondary agent arepreferred those having a viscosity of 0.5 to 10 mPa·s, especially 1.5 to5.0 mPa·s, more especially 1.5 to 4.0 mPa·s, measured at 20° C. withrespect to a 4% by weight aqueous solution of the completely hydrolyzedone. If the viscosity is less than 0.5 mPa·s, the effects as thesecondary agent are not sufficiently exhibited and, therefore, theinternal morphology of polymer particles obtained by suspensionpolymerization tends to be not sufficiently controlled (increase ofinternal voids of polymer particles is insufficient and also theobtained polymer particles become coarse). If the viscosity is more than10 mPa·s, the resin concentration of the aqueous solution (secondaryagent) cannot be raised, and also the fluidity of the aqueous solution(secondary agent) is deteriorated or the aqueous solution is gelled.

Upon the suspension polymerization, usually the secondary agent of thepresent invention and a known primary dispersing agent are added towater or hot water medium, and a vinyl monomer is then dispersed thereinand the polymerization is carried out in the presence of an oil-solublecatalyst. Examples of the primary dispersing agent are a cellulosederivative such as methyl cellulose, hydroxypropyl cellulose,hydroxylpropyl methyl cellulose or carboxymethyl cellulose, gelatin, awater-soluble polymer such as polyvinyl alcohol or polyvinylpyrrolidone, and the like. In particular, polyvinyl alcohol having adegree of hydrolysis of 65 to 90% by mole, preferably 68 to 89% by mole,and a degree of polymerization of 500 to 3,500 is preferably used as theprimary dispersing agent. Although varying depending on the kind of theprimary agent, it is preferable that the weight ratio of the primaryagent to the secondary agent is from 90/10 to 30/70, especially 80/20 to50/50.

The primary agent and the secondary agent may be added at one time inthe initial stage of the polymerization, or may be added stepwise duringthe polymerization.

Further, the secondary agent of the present invention may be used incombination with a cationic, anionic or non-ionic surfactant so long asthe effects of the present invention are not impaired.

The catalysts used in the suspension polymerization are not particularlylimited so long as they are oil-soluble catalysts. Examples of thecatalyst are, for instance, di-2-ethylhexyl peroxydicarbonate, γ-cumylperoxyneodecanoate, benzoyl peroxide, lauroyl peroxide, diisopropylperoxydicarbonate, α,α′-azobisisobutyronitrile,α,α′-azobis-2,4-dimethylvaleronitrile, acetylcyclohexylsulfonylperoxide, mixtures thereof, and the like.

Further, for the purpose of preventing scaling, an appropriate amount ofa water-soluble polymerization inhibitor such as ammonium thiocyanate ora nitrite may be added. A known anti-scaling agent such as “NOXOL WSW”or “NOXOL ETH” (which are products of CIRS Inc.) may also be used.

The polymerization temperature is suitably selected from the rangesknown to those skilled in the art in accordance with the degree of thepolymerization of desired vinyl polymers.

The monomers to be subjected to the suspension polymerization includevinyl chloride, monomers copolymerizable therewith, and other vinylcompounds. The secondary agent of the present invention is suitable fornot only homopolymerization of vinyl chloride, but also preparation ofcopolymers of vinyl chloride with monomers copolymerizable therewith,e.g., a vinylidene halide, vinyl benzoate, acrylic, methacrylic ormaleic acid and anhydride thereof, ethylene, propylene, styrene and thelike. Further, the secondary agent of the present invention can also beused for suspension polymerization of any vinyl compounds such asstyrene, methacrylic acid esters and vinyl acetate as well as thesuspension polymerization of vinyl chloride.

The present invention is more specifically explained below by means ofexamples, wherein all % and parts are by weight unless otherwise noted.

EXAMPLE 1

In 3.646 kg of isopropyl alcohol were copolymerized 1.246 kg ofpolyoxyethylene monoalyl ether (average number of moles of ethyleneoxide added: 15) and 7 kg of vinyl acetate for 8 hours with addingacetyl peroxide in amounts of 0.07% by mole (based on vinyl acetate) atthe time of starting the polymerization, 0.03% by mole (based on vinylacetate) after 2 hours, 0.03% by mole (based on vinyl acetate) after 4hours and 0.03% by mole (based on vinyl acetate) after 6 hours(polymerization conversion 97.3%). After expelling the remainingmonomers until the amount thereof became 0.06%, a solution of 6.6millimole % (based on vinyl acetate) of sodium hydroxide dissolved inmethanol was added and the hydrolysis was carried out at 35° C. for 2hours. The obtained polymer was dried to give a polyoxyethylenegroup-containing partially hydrolyzed vinyl ester resin (secondaryagent 1) as shown in-Tables 1 and 2.

The obtained resin (secondary agent 1) was dissolved as a dispersoid orsolute in water by a kneader to give an aqueous solution having aconcentration shown in Table 3. The dispersibility and storage stabilitythereof were measured by the following methods. The results of theevaluation are shown in Table 3.

(Dispersibility)

Deposition of the modified partially hydrolyzed vinyl ester resin,formation of gel and phase separation were visually checked.

(Storage Stability)

An aqueous solution was allowed to stand at 20° C. for 12 months, andthe state of dispersion (or dissolution) of the dispersoid or solute wasvisually observed to check occurrence of a change such as occurrence ofagglomeration or deposition.

(Cloud Point)

Cloud point was measured by an integrating sphere type turbidimeter(SEP-PT-706D made by Mitsubishi Chemical Corporation) at a rate oftemperature elevation of 1° C./minute.

Using a primary agent (A) (polyvinyl alcohol) and an aqueous solution ofsecondary agent 1 as shown in Table 4, a polymerization of vinylchloride was carried out in the following manner and the obtainedpolyvinyl chloride particles were evaluated with respect to theperformances as mentioned after.

An autoclave equipped with a stirrer was charged with 100 parts of vinylchloride monomer, 150 parts of water, 0.2 part of a dilute solution ofthe aqueous solution of secondary agent 1 shown in Table 3 which hadbeen diluted at the time of charging to a solid concentration of 10% inorder to raise the quantitativeness of charging (0.02 part in terms ofsolid oxyethylene group-containing vinyl ester-vinyl alcohol copolymer),0.08 part of a polyvinyl alcohol having a degree of polymerization of2,200 and a degree of hydrolysis of 80% by mole as the primary agent (A)and 0.2 part of lauroyl peroxide. Suspension polymerization was carriedout at 60° with stirring at 400 r.p.m. to give polyvinyl chlorideparticles, and the following evaluation of the polyvinyl chlorideparticles was conducted. The results are shown in Table 5.

(Bulk Density)

Measured according to JIS K 6721.

(Plasticizer absorptivity)

Into a planetary type mixer connected to a plastograph was placed amixture of 60 parts of the obtained polyvinyl chloride particles and 40parts of DOP (dioctyl phthalate). The kneading torque was measured everyhour with stirring the mixture at 80°, and the time elapsed until thetorque lowers was measured.

The evaluation was made according to the following criteria.

A: less than 3 minutes

B: 3 to less than 5 minutes

C: 5 minutes or more

(Remaining monomer)

A predetermined amount of the obtained polyvinyl chloride particles wasdissolved in THF (tetrahydrofuran), and the remaining vinyl chloridemonomer was determined by a gas chromatograph.

(Fish eye)

A 0.3 mm thick sheet was prepared by roll-mixing 100 parts of theobtained polyvinyl chloride particles, 50 parts of DOP (dioctylphthalate), 3 parts of dioctyl tin dilaurate and 1 part of zinc stearateat 155° C. for 3 minutes, and the number of fish eyes per 100 mm×100 mmwas measured.

The evaluation was made according to the following criteria.

A: 0 to 4 fish eyes

B: 5 to 10 fish eyes

C: 11 fish eyes or more

(Scaling)

After taking out a slurry of a polymer from the polymerization vessel,the state of scaling inside the vessel was visually observed andevaluated according to the following criteria.

A: No scale is present, and the metallic gloss inside the polymerizationvessel is observed.

B: The metallic gloss inside the polymerization vessel is not vivid.

C: Scale in the form of a film is observed on the entire inner surfaceof the polymerization vessel.

EXAMPLES 2 TO 10 AND COMPARATIVE EXAMPLE 1

Oxyalkylene group-containing partially hydrolyzed vinyl ester resins(secondary agents 2 to 7 and secondary agent 17) and a mercaptoalkylenegroup-containing partially hydrolyzed vinyl ester resin (secondary agent8) as shown in Tables 1 and 2 were produced according to the procedureof Example 1, and aqueous solutions shown in Table 3 were prepared andevaluated in the same manner. In the production of secondary agent 8, aboth end thiol-modified derivative of polyethylene glycol was usedinstead of polyoxyethylene monoallyl ether used in Example 1.

The results of evaluation are shown in Table 3.

Further, polymerization of vinyl chloride was carried out according tothe procedure of Example 1 by using the primary agent (A) and an aqueoussolution of each of secondary agents 2 to 8 as shown in Table 4. Theobtained polyvinyl chloride particles were evaluated in the same manneras in Example 1. The results of the evaluation are shown in Table 5.

The secondary agent 17 obtained in Comparative Example 1 was poor indispersibility as shown in Table 3 and, therefore, no polymerization ofvinyl chloride was conducted.

EXAMPLE 11

In 3.646 kg of isopropyl alcohol were copolymerized 1.246 kg ofpolyoxyethylene monoallyl ether (average number of moles of ethyleneoxide added: 15), 3.8 g of a 60% methanol solution of monomethyl maleateand 7 kg of vinyl acetate for 7 hours, while continuously addingdropwise 102 g of a 60% methanol solution of monomethyl maleate andadding acetyl peroxide in amounts of 0.07% by mole (based on vinylacetate) at the time of starting the polymerization, 0.03% by mole(based on vinyl acetate) after 2 hours, 0.03% by mole (based on vinylacetate) after 4 hours and 0.03% by mole (based on vinyl acetate) after6 hours (polymerization conversion 95%). After expelling the remainingmonomers until the amount thereof became 0.08%, a solution of 6.6millimole % (based on vinyl acetate) of sodium hydroxide dissolved inmethanol was added and the hydrolysis was carried out at 35° C. for 2hours. The obtained polymer was dried to give a polyoxyethylenegroup-containing partially hydrolyzed vinyl ester resin (secondary agent9) as shown in Table 1.

The obtained resin (secondary agent 9) was dissolved in water by akneader to give an aqueous solution having a concentration shown inTable 3. The dispersibility and storage stability thereof were measuredin the same manner as in Example 1. The results of the evaluation areshown in Table 3.

EXAMPLES 12 to 20

Partially hydrolyzed vinyl ester resins containing oxyalkylene group andionic group (secondary agents 10 to 16) as shown in Tables 1 and 2 wereproduced according to the procedure of Example 1, and aqueous solutionsshown in Table 3 were prepared and evaluated in the same manner as inExample 1. The results of evaluation are shown in Table 3.

Further, polymerization of vinyl chloride was carried out according tothe procedure of Example 1 by using the primary agent (A) and an aqueoussolution of each of secondary agents 10 to 16 as shown in Table 4. Theobtained polyvinyl chlorides were evaluated in the same manner as inExample 1.

The results of the evaluation of polyvinyl chloride polymerization inExamples 12 to 20 are shown in Table 5.

TABLE 1 Oxyalkylene Mercaptoalkylene group group Ionic group ContentContent Content (mole (mole (mole Kind %) Kind %) Kind %) Secondaryagent 1 I-a 2 — — — — Secondary agent 2 I-a 2 — — — — Secondary agent 3I-a 2 — — — — Secondary agent 4 I-b 2 — — — — Secondary agent 5 I-c 1 —— — — Secondary agent 6 I-d 3 — — — — Secondary agent 7 I-a 2 — — — —Secondary agent 8 — — II 0.6 — — Secondary agent 9 I-a 2 — — III 0.6Secondary agent 10 I-a 2 — — IV 0.4 Secondary agent 11 I-a 1 — — V 0.6Secondary agent 12 I-a 2 — — VI 0.2 Secondary agent 13 I-b 2 — — VII 0.5Secondary agent 14 I-c 2 — — VIII 0.7 Secondary agent 15 I-d 3 — — III0.8 Secondary agent 16 I-a 2 — — III 0.6 Secondary agent 17 I-a   0.3 —— — — (Notes) The kinds of oxyalkylene group, mercaptoalkylene group andionic group are shown below, wherein the number in the parenthesesdenotes the average number of moles of addition of the group. I-a:Polyoxyethylene monoallyl ether (n = 15) I-b: Polyoxyethylene acrylamide(n = 30) I-c: Polyoxyethylene vinyl ether (n = 50) I-d: Polyoxyethylenemonoallyl ether (n = 8) II: Thiol-modified compound that the both endsare modified with thiol, HS-PEO-SH (molecular weight 2,000) III:Monomethyl maleate IV: Itaconic acid V: 2-Mercaptopropionic acid VI:Sodium allylsulfonate VII: N-vinylimidazole VIII: Sodiummethallylsulfonate

(Notes) The kinds of oxyalkylene group, mercaptoalkylene group and ionicgroup are shown below, wherein the number in the parentheses denotes theaverage number of moles of addition of the group.

I-a: Polyoxyethylene monoallyl ether (n=15)

I-b: Polyoxyethylene acrylamide (n=30)

I-c: Polyoxyethylene vinyl ether (n=50)

I-d: Polyoxyethylene monoallyl ether (n=8)

II: Thiol-modified compound that the both ends are modified with thiol,HS-PEO-SH (molecular weight 2,000)

III: Monomethyl maleate

IV: Itaconic acid

V: 2-Mercaptopropionic acid

VI: Sodium allylsulfonate

VII: N-vinylimidazole

VIII: Sodium methallylsulfonate

TABLE 2 Degree of Clound hydrolysis point Viscosity x y Equation at 4%(mole %) (° C.) (I)* (mPas) Secondary agent 1 45 45 satisfied 3Secondary agent 2 45 43 satisfied 1 Secondary agent 3 45 47 satisfied 5Secondary agent 4 45 49 satisfied 3 Secondary agent 5 50 52 satisfied 2Secondary agent 6 45 47 satisfied 5 Secondary agent 7 60 75 satisfied 3Secondary agent 8 58 70 satisfied 3 Secondary agent 9 45 47 satisfied 3Secondary agent 10 45 48 satisfied 5 Secondary agent 11 35 25 satisfied2 Secondary agent 12 40 40 satisfied 1 Secondary agent 13 50 75satisfied 2 Secondary agent 14 45 48 satisfied 3 Secondary agent 1560 >80 satisfied 3 Secondary agent 16 45 45 satisfied 0.3 Secondaryagent 17 45 ** ** 3 (Notes) *1n y > 0.042x + 1.0 **It was impossible toprepare a 30% aqueous solution (due to separation).

The degree of hydrolysis denotes a degree of hydrolysis of the vinylacetate component.

The viscosity at 4% denotes a viscosity value obtained by completelyhydrolyzing the copolymer and measuring the viscosity of a 4% aqueoussolution of the complete hydrolysis product at 20° C.

TABLE 3 Aqueous solution Concen- tration Storage Kind (%) Dispersibilitystability Ex. 1 Secondary agent 1 40 No separation, no No changedeposition, etc. Ex. 2 Secondary agent 2 40 No separation, no ″deposition, etc. Ex. 3 Secondary agent 3 40 No separation, no ″deposition, etc. Ex. 4 Secondary agent 1 10 No separation, no ″deposition, etc. Ex. 5 Secondary agent 4 45 No separation, no ″deposition, etc. Ex. 6 Secondary agent 5 40 No separation, no ″deposition, etc. Ex. 7 Secondary agent 6 30 No separation, no ″deposition, etc. Ex. 8 Secondary agent 7 40 No separation, no ″deposition, etc. Ex. 9 Secondary agent 7 5 No separation, no ″deposition, etc. Ex. 10 Secondary agent 8 10 No separation, no ″deposition, etc. Ex. 11 Secondary agent 9 40 No separation, no ″deposition, etc. Ex. 12 Secondary agent 10 8 No separation, no ″deposition, etc. Ex. 13 Secondary agent 11 30 No separation, no ″deposition, etc. Ex. 14 Secondary agent 12 45 No separation, no ″deposition, etc. Ex. 15 Secondary agent 13 15 No separation, no ″deposition, etc. Ex. 16 Secondary agent 14 40 No separation, no ″deposition, etc. Ex. 17 Secondary agent 15 5 No separation, no ″deposition, etc. Ex. 18 Secondary agent 9 3 No separation, no ″deposition, etc. Ex. 19 Secondary agent 12 3 No separation, no ″deposition, etc. Ex. 20 Secondary agent 16 40 No separation, no ″deposition, etc. Com. Secondary agent 17 40 There is deposite. ‡ Ex. 1‡The storage stability was not evaluated since the dispersibility wasbad.

TABLE 4 Primary agent (A) Secondary agent Degree of Degree of Amountpolymer- hydrolysis Amount Kind (part)* ization (mole %) (part) Ex. 1Aqueous solution 0.02 2400 80 0.08 of secondary agent 1 Ex. 2 Aqueoussolution 0.02 2200 80 0.08 of secondary agent 2 Ex. 3 Aqueous solution0.02 700 72 0.01 of secondary agent 3 Ex. 4 Aqueous solution 0.02 220078 0.06 of secondary agent 1 Ex. 5 Aqueous solution 0.02 2200 76 0.07 ofsecondary agent 4 Ex. 6 Aqueous solution 0.04 3000 80 0.04 of secondaryagent 5 Ex. 7 Aqueous solution 0.02 2206 76 0.07 of secondary agent 6Ex. 8 Aqueous solution 0.03 800 72 0.08 of secondary agent 7 Ex. 9Aqueous solution 0.03 800 72 0.08 of secondary agent 7 Ex. 10 Aqueoussolution 0.03 800 72 0.08 of secondary agent 8 Ex. 11 Aqueous solution0.02 2200 80 0.08 of secondary agent 9 Ex. 12 Aqueous solution 0.02 70072 0.07 of secondary agent 10 Ex. 13 Aqueous solution 0.02 1700 80 0.08of secondary agent 11 Ex. 14 Aqueous solution 0.02 2400 80 0.08 ofsecondary agent 12 Ex. 15 Aqueous solution 0.04 3000 80 0.04 ofsecondary agent 13 Ex. 16 Aqueous solution 0.02 2200 76 0.07 ofsecondary agent 14 Ex. 17 Aqueous solution 0.03 800 72 0.08 of secondaryagent 15 Ex. 18 Aqueous solution 0.02 2200 80 0.08 of secondary agent 9Ex. 19 Aqueous solution 0.02 2200 80 0.08 of secondary agent 12 Ex. 20Aqueous solution 0.02 2200 80 0.08 of secondary agent 16 *Denote theamount of solid matter in the aqueous solution.

TABLE 5 Bulk Remaining density Plasticizer monomer (g/cc) absorptivity(p.p.m.) Fish eye Scaling Example 1 0.552 A 0.3 A A Example 2 0.532 A0.3 A A Example 3 0.600 A 0.4 A A Example 4 0.530 A 0.3 A A Example 50.538 A 0.6 A A Example 6 0.540 B 0.4 B A Example 7 0.549 A 0.3 A AExample 8 0.530 A 0.2 A A Example 9 0.530 A 0.2 A A Example 10 0.530 A0.2 A A Example 11 0.559 A 0.3 A A Example 12 0.531 A 0.2 A A Example 130.539 A 0.2 A A Example 14 0.563 A 0.3 A A Example 15 0.549 A 0.7 A AExample 16 0.545 A 0.4 A A Example 17 0.530 A 0.2 A A Example 18 0.554 A0.2 A A Example 19 0.565 A 0.3 A A Example 20 0.532 A 0.9 A A

INDUSTRIAL APPLICABILITY

The aqueous solution of partially hydrolyzed vinyl ester resin of thepresent invention has an excellent storage stability and is a stableaqueous solution such that no resin is deposited even if diluted withwater to a low concentration (is an aqueous solution having a goodmiscibility with water). It is very useful for use as a secondary agentfor suspension polymerization of vinyl compounds, and other uses such asadhesive and plasticizer.

What is claimed is:
 1. An aqueous solution of a partially hydrolyzedoxyalkylene group-containing vinyl ester resin having a degree ofhydrolysis of 20 to 60% by mole, the concentration of the partiallyhydrolyzed oxyalkylene group-containing vinyl ester resin in the aqueoussolution being from 30 to 50% by weight, wherein said partiallyhydrolyzed vinyl ester resin is prepared by copolymerizing a vinyl esterwith an unsaturated monomer having an oxyalkylene group of the followingformula (2):

 wherein R¹, R², R³ and R⁴ are the same or different, and each of R¹,R², R³ and R⁴ is selected from the group consisting of a hydrogen atomand an alkyl group, n is a positive number and m is 0 or a positivenumber, and 8≦n+m≦20, and partially hydrolyzing the resulting vinylester copolymer, the content of said oxyalkylene group being from 0.5 to5.0% by mole, said partially hydrolyzed vinyl ester resin satisfying theequation (I): 1n y>0.042x+1.0  (1)  wherein y is the cloud point (° C.)of a 30% by weight aqueous solution of said partially hydrolyzed vinylester resin, and x is the degree of hydrolysis (% by mole) of saidpartially hydrolyzed vinyl ester resin, and the viscosity at 20° C. of a4% by weight aqueous solution of a complete hydrolysis product of saidpartially hydrolyzed vinyl ester resin is from 1.5 to 5.0 mPa·s, saidmonounsaturated monomer having an oxyalkylene group selected from thegroup consisting of oxyalkylene groups of the following formulas (4) to(7):

 wherein R¹, R², R³, R⁴, n, m, and n+m are as defined above, A is aphenylene group or a substituted phenylene group, Y is a hydrogen atomor a methyl group, and 1 is 0 or an integer of not less than 1,

wherein A, Y, R¹, R², R³, R⁴, 1, n, m, and n+m are as defined above, andY³ is selected from the group consisting of a hydrogen atom, a methylgroup, a group of formula (2) above, and a group of the followingformula (1):

wherein R¹, R², R³, R⁴, n, m, and n+m are as defined above, and X¹ andX² are the same or different, and each of X¹ and X² is selected from thegroup consisting of an oxygen atom and a sulfur atom,

wherein Y, R¹, R², R³, R⁴, n, m, and n+m are as defined above, and

 wherein A, R¹, R², R³, R⁴, 1, n, m, and n+m are as defined above. 2.The aqueous solution of claim 1, which is used as a secondary agent forsuspension polymerization of vinyl compounds.
 3. The aqueous solution ofclaim 1 or 2, wherein said partially hydrolyzed vinyl ester resincontains an ionic group.
 4. The aqueous solution of claim 1, wherein theconcentration of the partially hydrolyzed oxyalkylene group-containingvinyl ester resin in the aqueous solution is from 30 to 40% by weight.5. The aqueous solution of claim 1, wherein the cloud point y (° C.) ofa 30% by weight aqueous solution of said partially hydrolyzed vinylester resin is 25° C. or higher.